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Million-year archive European scientists have designed and built a disk they say could store data for a million years, potentially keeping a record of humanity long after we're gone.

For centuries humans have recorded their achievements in various forms; from cave paintings and rock etching through to print and electronic media. But in the long term, all our existing methods of storage have a limited shelf life.

Digital storage systems can only retain their data for a matter of decades, archival paper can only be expected to last up to 500 years, while text engraved in a marble slab will eventually erode away, write nanotechnologist Jeroen de Vries from the University of Twente, The Netherlands, and colleagues.

"If we want to preserve anything about the human race which can outlast the human race itself, we require a data storage medium designed to last for one million to one billion years," they write in paper posted on the arXiv.org research article server.

To meet this need, the researchers built a disk made of chemically inert silicon nitride, a compound used to make parts of car engines, as an insulator in manufacturing integrated circuits and more.

Into this disk, they embedded tungsten, a hard, dense metal widely used in incandescent light bulb filaments and X-ray tubes and other applications.

The researchers stored their data by laying down the tungsten in the form of a QR code, a two-dimensional bar code often used to deliver information to smart phones, which was then covered in a thin layer of silicon nitride.

Simulating a million years

Instead of waiting a million years to see if the data really did survive, for experimental purposes the researchers simulated the passing of time by heating up the disk.

The basis for this short cut is a formula called the Arrhenius law, which shows the relationship between temperature and the rates of chemical reactions.

Using the Arrhenius law, the researchers calculated that subjecting their chip to a temperature of 188°C for an hour would be equivalent to a million years at 27°C.

In fact, after a series of experiments the researchers found that the disks survived significantly higher temperatures of up to 440°C for two hours.

These temperatures resulted in cracking of the silicon-nitride coating. At higher temperatures this cracking hindered the reading back of the data through an optical microscope they said, although the QR codes themselves "are not visibly damaged and the tungsten is still present," they write.

Although more work is needed to solve the cracking problem, and to test the disk against things such as acid, wind and sand, de Vries and colleagues say they are encouraged.

"The initial attempt to create a medium containing embedded data which is able to survive for one million years is promising," they write. "At … temperatures which correspond to a storage time of 1 million years or more, the data carrier survives."